Mold assembly for making an expanded polystyrene article

ABSTRACT

A mold assembly and method for molding a substantially hemispherical construct from pre-expanded polystyrene beads. The mold assembly includes a female half mold; a mating male half mold; a first male mold insert mountable on the male half mold and having a continuous, peripheral, beveled edge; and a second male mold insert mountable on the first male mold insert. For forming a construct having an impact-resistant exterior layer and an energy-absorbing interior layer, such as a motorcyclist safety helmet, the beads are initially molded under heat and compression between the female half mold and the first insert to form a first intermediate product of a first volume having a continuous, peripheral, beveled edge; said product is thereafter molded under heat and compression between the female half mold and the second insert to a second, reduced volume to form a compressed, second intermediate product, the beveled edge of the first intermediate product serving to uniformly distribute the force applied thereto. The second intermediate product is then remolded to the same volume to improve volume stability, and thereafter backfilled between the male half mold and the female half mold with additional pre-expanded polystyrene beads to form an energy-absorbing inner layer.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] None, however, Applicant filed Disclosure Document Number 445113on Oct. 7, 1998, which document concerns this application; therefore, byseparate paper it is respectfully requested that the document beretained and acknowledgement thereof made by the Examiner (MPEP 706).

STATEMENT REGARDING FEDERALLY APPROVED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] This invention relates generally to expanded polystyreneconstructs having a high-impact resistance and strength without anunacceptable increase in brittleness, and a method for making the same.More particularly, this invention relates to such constructs that arecreated by a molding process that includes, as an intermediary step, theimparting of a cam or beveled edge surface to the construct preparatoryto compressing the construct to high density. The beveled edge surfaceimparted to the construct serves to uniformly distribute the forcesapplied during the compression step even over relatively large angulardeviations from the mold parting line, thereby permitting the molding ofa single large construct that formerly, prior to this invention, wouldhave required the molding and combining of several smaller, partialconstructs. Thus, the disclosed method is particularly useful in themolding of polystyrene motorcyclist and bicyclist safety helmets andpolystyrene shipping boxes such as those commonly used for shipping icedfish. This invention also provides molding apparatus adapted for moldingconstructs of the type described.

[0005] 2. Background Art.

[0006] A method for molding an expanded, highly impact-resistant,polystyrene construct from polystyrene beads was disclosed in U.S. Pat.No. 5,718,968 to P. W. Cutler et al., which by this reference isincorporated herein. The polystyrene beads include a thin outer shell ofpolystyrene and a hollow interior that includes a blowing agent, such aspentane, for example. According to the method, the beads were firstpre-expanded by application of heat through hot air or steam, whichcaused the blowing agent to vaporize and expand the beads. The beadswere then cooled, which caused the beads to have reduced internalpressure. The pre-expanded beads were next placed into a mold assemblywhere they were subjected to heat and pressure for molding to a firstvolume. The molded article was then rapidly cooled in the mold assembly,thereby causing the vaporized blowing agent within the beads to condenseand create a pressure less than atmospheric inside the beads.Thereafter, the molded product with beads having low internalpressure-was immediately subjected to compression within the moldassembly to a second volume, less than the first volume. This resultedin a single layer construct that had memory shape and was particularlysuited for acoustic and thermal insulation. Alternatively, additionallayers were molded within the mold assembly by adding beads to the firstmolding step and then molding together the originally-molded layer withthe additional beads. This yielded a layered construct wherein eachlayer had a different density than the other layers and each layer had adensity higher than the density of the beads from which it was molded,except when a last layer was a backfill layer of density equal to thatof the beads from which it was molded. The layered construct was volumestable, high density, high strength, and highly impact resistant.

[0007] When this method was used to mold a safety helmet for amotorcyclist or bicyclist, the outermost layer had the highest density,while inner layers had lower densities to absorb impact forces tominimize transmission of these forces through the construct. Such ahelmet, being substantially hemispherical and having a 360 degreecircumference, was thought to require molding in at least fiveparts—crown, front, back, and two sides—which thereafter were assembledtogether in a single mold and finally molded together. This was becauseit had been found that the compression process was less effective whenthe pressure is applied at angles between 46 degrees and 89 degrees tothe parting line of the mold. It was theorized that compression pressurewas diffused so that the compression ratio rapidly diminished withpressure applied at angles more than 45 degrees with respect to theparting line of the mold.

[0008] There remains a need, therefore, for a method and mold assemblyfor molding pre-expanded polystyrene beads that permits molding asubstantially hemispherical polystyrene construct as a whole, in asingle, integrated molding process, thereby eliminating the need forfirst molding two or more individual component parts thereof and thecombining of the parts through an additional molding step. There alsoremains a need for expanded polystyrene constructs that are produced bythe method and mold assembly described herein, which feature high impactresistance and strength without an unacceptable increase in brittleness,and which can be molded in substantially hemispherical shapes in asingle, integrated molding process. These needs are fulfilled by thepresent invention.

SUMMARY OF THE INVENTION

[0009] A method and apparatus are provided for molding an expandedpolystyrene bead construct within a mold assembly. The mold assemblyincludes a female half mold having a first, continuous, peripheral edgesurface and an interior surface configured to impart a desired exteriorsurface to the construct. The mold assembly further includes a male halfmold having a second, peripheral edge surface in mating alignment withthe first peripheral edge surface when the female half mold and the malehalf mold are aligned on an alignment axis. The mold assembly alsoincludes a first male mold insert that is mountable on the male halfmold. When the male half mold, with the first male mold insert mountedthereon, is inserted into the female half mold, the space between thefemale half mold and the first male insert defines a first volume. Themold assembly also includes a second male mold insert, mountable on thefirst male mold insert, such that when the male half mold, with thefirst and second male mold inserts mounted thereon, is inserted into thefemale half mold, the space between the female half mold and the secondmale mold insert defines a second volume, which is less than the firstvolume. The first male mold insert has a third, beveled, continuous edgesurface for engaging an outer, peripheral portion of the preexpandedpolystyrene beads that are to be molded within the mold assembly, and towhich portion it imparts a beveled edge. Preferably the beveled edgesurface of the first male mold insert is deviated at least 45 degrees,but not more than 60 degrees, from a mold parting line normal to thealignment axis. In a preferred embodiment, for mounting the second malemold insert over the first male mold insert, the first male mold inserthas a plurality of upstanding alignment pins and the second male moldinsert has a plurality of second apertures in mating alignment with saidalignment pins, and the female half mold similarly has a plurality ofthird apertures in mating alignment with said alignment pins.

[0010] In a first embodiment, the method includes filling the femalehalf mold with pre-expanded polystyrene beads of a predetermineddensity; mounting the first male mold insert on the male half mold;molding the beads under applied heat and pressure by forcing the firstmale mold insert against the beads to fuse the beads together to form afirst intermediate product of a first volume having a continuous,beveled edge surface formed between the beveled edge surface of thefirst male mold insert and the peripheral edge surface of the femalehalf mold; rapidly cooling the fused first intermediate product towithin a subplasticizing temperature temperature (usually between 160and 180 degrees F.) to cause lower than atmospheric pressure within thebeads of the first intermediate product; mounting the second male moldinsert on the first male mold insert; and compressing the cooled firstintermediate product between the second male mold insert and the femalehalf mold to a second, reduced volume, before the low pressureconditions within the beads equilibrate to ambient conditions, toproduce a single-layer, fused, expanded bead body of at least 200percent higher density than the predetermined density of thepre-expanded beads. The reason for rapidly cooling the firstintermediate product to wthin a plasticizing temperature range is sothat the temperature of the intermediate product will be low enough toescape the post expansion that would follow if the termperature is toohigh and, at the same time, avoid the cell wall damage that would occurduring the subsequent compression if the temperature is too low.

[0011] In a second embodiment, for molding a more volume-stabilized,single-layer, polystyrene bead construct, the method includes thepreceding series of acts followed by the additional act of remolding thecooled intermediate product under heat and compression between thesecond male mold insert and the female half mold to a second, reducedvolume, before the low pressure conditions within the beads equilibrateto ambient conditions, to produce a fused, expanded bead body of atleast 200 percent higher density than the predetermined density of thepre-expanded beads.

[0012] In a third embodiment, for molding a layered, expandedpolystyrene bead construct, the method includes filling the female halfmold with pre-expanded polystyrene beads of a predetermined density;mounting the first male mold insert on the male half mold; molding thebeads under applied heat and pressure by forcing the first male moldinsert against the beads to fuse the beads together to form a firstintermediate product of a first volume having a continuous, beveled edgesurface formed between the beveled edge surface of the first male moldinsert and the peripheral edge surface of the female half mold; rapidlycooling the fused first intermediate product to within a subplasticizingtemperature range to cause lower than atmospheric pressure within thebeads of the first intermediate product; mounting the second male moldinsert on the first male mold insert; and compressing the cooled firstintermediate product between the second male mold insert and the femalehalf mold to a second, reduced volume, before the low pressureconditions within the beads equilibrate to ambient conditions, toproduce a single-layer, fused, expanded bead body of at least 200percent higher density than the predetermined density of thepre-expanded beads; removing the second male mold insert from the firstmale mold insert; and adding pre-expanded polystyrene beads to the moldassembly and remolding the added beads between the female half mold andthe male half mold under heat and compression to cause fusion of theadded beads at an interface to the expanded bead body to form a layeredconstruct comprising at least two layers of beads wherein the beads havedifferent densities. In a fourth embodiment, a backfilled, layeredconstruct is molded by a method that includes filling the female halfmold with pre-expanded polystyrene beads of a predetermined density;mounting the first male mold insert on the male half mold; molding thebeads under applied heat and pressure by forcing the first male moldinsert against the beads to fuse the beads together to form a firstintermediate product of a first volume having a continuous, beveled edgesurface formed between the beveled edge surface of the first male moldinsert and the peripheral edge surface of the female half mold; rapidlycooling the fused first intermediate product to within a subplasticizingtemperature range to cause lower than atmospheric pressure within thebeads of the first intermediate product; mounting the second male moldinsert on the first male mold insert; and compressing the cooled firstintermediate product between the second male mold insert and the femalehalf mold to a second, reduced volume, before the low pressureconditions within the beads equilibrate to ambient conditions, toproduce a single layer, fused, expanded bead body of at least 200percent higher density than the predetermined density of thepre-expanded beads; remolding the cooled intermediate product under heatand compression between the second male mold insert and the female halfmold to a second, reduced volume, before the low pressure conditionswithin the beads equilibrate to ambient conditions, to produce a fused,expanded bead body of at least 200 percent higher density than thepredetermined density of the pre-expanded beads; removing the secondmale mold insert from the first male mold insert;-and addingpre-expanded polystyrene beads to the mold assembly and remolding theadded beads between the female half mold and the male half mold underheat and compression to cause fusion of the added beads at an interfaceto the expanded bead body to form a layered construct comprising atleast two layers of beads wherein the layers have different densities.The latter embodiment of the method is particularly suited for moldingsubstantially hemispherical constructs having a 360 degreecircumferential edge, such as bicyclist and motorcyclist safety helmets,and packing crates.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is an exploded, perspective view of a mold assembly of anillustrative embodiment of the invention for molding a motorcyclistsafety helmet, showing the male half mold, female half mold, and thefirst male mold insert thereof aligned on an alignment axis A-A;

[0014]FIG. 2 is a perspective view of the male half mold thereof;

[0015]FIG. 3 is a top plan view of the first male mold insert thereof;

[0016]FIG. 4 is a perspective view of the first male mold insert mountedon the male half mold thereof;

[0017]FIG. 5 is a perspective view of the second male mold insertthereof;

[0018]FIG. 6 is a perspective view of the second male mold insertmounted on the first male mold insert and male half mold thereof; and

[0019]FIG. 7 is a fragmentary, cross-sectional view of a crown portionof said mold assembly in the configuration depicted in FIG. 6, takenalong line 6-6 thereof, and of the hemispherical portion of the femalehalf mold when the mold assembly is in a closed position.

[0020]FIG. 8 is a bottom plan view of a first intermediate productmolded between the female half mold and the first male mold insert ofFIG. 1.

[0021]FIG. 9 is a bottom plan view of a second intermediate productmolded from the first intermediate product by compression between thefemale half mold and the second male mold inserts of FIGS. 1-6.

[0022]FIG. 10 is a bottom plan view of a backfilled construct formedfrom the second intermediate product between the female half mold andthe male half mold of FIGS. 1-6 after removal of the first and secondmale mold insert from the male half mold.

[0023]FIG. 11 is a cross-sectional view of the first intermediateproduct of FIG. 8 taken along line 11-11.

[0024]FIG. 12 is a cross-sectional view of the second intermediateproduct of FIG. 9 taken along line 12-12.

[0025]FIG. 13 is a cross-sectional view of the backfilled, layeredconstruct of FIG. 10 taken along line 13-13.

[0026]FIG. 14 is an enlarged, schematic view of a section S taken fromFIG. 13, showing the three, fused, expanded polystyrene layers thereof(P1—highest density layer; P2—intermediate density layer; P3—backfilled, energy absorbing layer).

[0027]FIG. 15 is a perspective view of a motorcyclist safety helmet(visor removed) that incorporates a multilayer polystyrene constructmolded on the mold assembly depicted in FIGS. 1-5.

[0028]FIG. 16 is a perspective view of an expanded polystyrene packingcrate molded by the process described herein.

[0029]FIG. 17 is a perspective view of an expanded polystyrene edgeprotector molded by the process described herein.

[0030]FIG. 18 is a perspective view of an expanded polystyrene cornerprotector molded by the process described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0031] Referring to FIG. 1, an illustrative embodiment of four componentparts of a mold assembly, denoted generally by the numeral 10, formolding a motorcyclist safety helmet 12, are shown in exploded,perspective view—namely, a female half mold 14, a male half mold 16, afirst male mold insert 18 placed over the male half mold 16; a secondmale mold insert 20, which is also part of the mold assembly 10, isinsertable over the first male mold insert 18, as described below. Allfour components are aligned on an axis A-A. The female half mold 14includes a flat plate portion 14P normal to axis A-A and a centrallydisposed, substantially hemispherical portion 14H that extends axiallyaway from the male half mold 16. The hemispherical portion 14H has aninterior surface that is configured to impart a desired exterior surfaceto a mold construct for a motorcyclist safety helmet 12. The male halfmold 16 has a flat plate portion 16P normal to axis A-A and a centrallydisposed, substantially hemispherical portion 16H that extends axiallytowards the female half mold 14. A mold parting line P-P′ is defined asany straight line normal to axis A-A and lying in a plane that containsapposed, engaged surfaces of plate portions 14P, 16P when the moldassembly 10 is in a closed position with the substantially hemisphericalportion 16H of the male half mold 16 inserted inside of thesubstantially hemispherical portion 14H of the female half mold 14.

[0032] Referring now to FIG. 2, the male half mold 16 is shown inenlarged, perspective view, removed from the remainder of the moldassembly 10. It may be seen that the male half mold 16 includes aconvex, crown portion 16C integral with, and surrounded by, aperipheral, relatively narrow, upturned flange portion 16F, the narrowspace between the flange portion 16F and the crown portion 16C defininga peripheral well 16W. The flange portion 16F is somewhat raised at thefront relative to the sides and rear of the flange portion 16F,corresponding to the brow portion 12B of a motorcyclist safety helmet12, depicted in FIG. 15, as molded on the illustrated mold assembly 10.

[0033] Referring to FIG. 3, the first male mold insert 18 has a convex,crown portion 18C integral with, and surrounded by, a beveled,continuous peripheral edge 18E. Four alignment pins 18P, extend axiallyfrom the crown portion 18C and are configured for insertion into matingapertures 20A, 14A in the second male insert 20 and in the female halfmold 14, respectively. The crown portion 18C and the edge 18E are sizedand configured such that the insert 18 mounts snugly on the male halfmold 16 with the edge 18E overlying the well 16W of the male half mold16. As shown in FIG. 4, when the first male mold insert 18 is so mountedon the male half mold 16, the beveled edge 18E extends radially inwardfrom the flange 16, and axially away from the mold parting line P-P′ byangle R defined by a line OX tangent to the beveled edge 18E and theparting line P-P′, where O is a peripherally-disposed point ofintersection of said tangent line with the parting line P-P′.Preferably, R is between 45 and 60 degrees.

[0034]FIG. 5 shows that the second mold insert 20 is substantiallyhemispherical and, unlike the male half mold 16 and the first maleinsert 16, has no peripheral flange or beveled edge. As shown in FIG. 6,the second mold insert 20 is sized and configured for mounting atop thefirst male mold insert 18 (shown in phantom). Thus, as shown in FIG. 7,when the mold assembly 10 is closed, the distance D₁, and hence thevolume, between the substantially hemispherical portion 14H of thefemale half mold 14 and the second male mold insert is least; when thesecond mold insert 20 is removed and only the first male mold insert ismounted on the male half mold, the distance D₂, and hence the volumebetween portion 14H and the first male mold insert 18 is somewhatlarger; and when both inserts 18, 20 are removed, the distance D₃, andhence the volume, between portion 14H and the male half mold 16 is thelargest.

[0035] In use, for molding a motorcyclist safety helmet 12, thesubstantially hemispherical portion 14H of the female half mold 14 isfilled with pre-expanded polystyrene beads (not shown) of apredetermined density. The first male mold insert 18 is mounted on themale half mold 16. Once filled, the mold is clamped shut. The beads aremolded under applied heat and pressure by forcing the male mold insertagainst the beads to fuse the beads together to form a firstintermediate product 32 of a first volume, depicted in FIGS. 8 and 11.Preferably, the molding is carried out at a pressure from about 9 toabout 12 psi, and the product being molded is allowed to dwell at atemperature of from about 100 degrees C. to about 110 degrees C. forfrom about 15 to about 30 seconds. The first intermediate product 30 isthen rapidly cooled by the introduction of water into the mold assembly.The first intermediate product 30 is allowed to dwell with the coolingwater for a sufficient time to enable the blowing agent within the beadsto once again liquefy, typically, less than 2 minutes, depending on thethickness of the molded part. The pressure is then relieved.

[0036] With the first intermediate product 30 still within the femalehalf mold 14, the second male mold insert 20 is mounted over the firstmale insert 18 with the alignment pins 18P inserted through thealignment apertures 20A, and the mold assembly 10 is closed. The firstintermediate product 30 is substantially hemispherical, but has acontinuous, beveled edge 30B, as may best be seen in FIG. 11. When themold assembly 10 is in closed position, the peripheral edge 20E of thesecond mold insert 20 engages the beveled edge 30B of the firstintermediate product 30. Thus, when next pressure is applied to the moldassembly 10 to compress the cooled first intermediate product 30 from afirst volume to a second, lesser volume, the beveled edge 30B serves touniformly distribute the force applied by the peripheral edge 20E. Themold assembly 10 is clamped shut during this step for at least 3seconds. This operation produces a relatively thin, second intermediateproduct 32, depicted in FIGS. 9 and 12, which is a fused expanded beadbody of at least 200 percent higher density than the predetermineddensity of the pre-expanded beads.

[0037] Next, the cooled, second intermediate product 32 is remoldedunder heat and compression between the second male insert 20 and thefemale half mold 14 to a second, reduced volume before the low pressureconditions within the beads equilibrate to ambient conditions; theremolded product is then cooled as before. This operation significantlyincreases the volume stability of the molded construct and results in aconstruct consisting of two layers.

[0038] The second male mold insert 20 and the first male mold insert 18are then removed from the male half mold 16. The female half mold 14 isagain filled with pre-expanded polystyrene beads for remolding the addedbeads between the female half mold 14 and the male half mold 16 underheat and compression to cause fusion of the added beads at an interfaceto the expanded bead body to form a backfilled, layered construct 34,here comprising two layers, l₁ (high density) and l₂ (back fill, lowdensity), as shown in FIG. 14. The backfilled, layered construct 34 iscooled as before and removed from the mold assembly 10. A suitableexterior finish is thereafter applied to the backfilled, layeredconstruct 34 in making the helmet 12. In this manner, a substantiallyhemispherical construct 34 can be molded without the necessity for firstmolding individual components thereof (crown, front, back and two sides)and the concomitant necessity thereafter for combining them in anadditional molding operation.

[0039] It will be understood that the above-described process formolding a multilayer polystyrene construct for use in a motorcyclistsafety helmet can be adapted to the making of a variety of other objectsby appropriate adjustments to the shapes and sizes of the componentparts of the mold assembly. Such other objects include, for example,bicyclist safety helmets, packing crates, corner protectors, motorvehicle dashboard components, and, in general, any object in which asturdy, impact-resistant, expanded polystyrene exterior layer is to becombined with a relatively soft, energy absorbing, interior layer. Forexample, a a packing crate 100, including a chest 100C and a lid 100L,depicted in FIG. 16, an edge protector 110 (three-layered), useful forshipping furniture, for instance, and depicted in FIG. 17, and a cornerprotector 112 (two-layered), for protecting a window during shipping andinstallation, depicted in FIG. 18, were each made according to theabove-described process. In the case of the packing crate chest 100C, ahigh density layer 100K surrounds a low density, back-filled layer 100J.

[0040] Moreover, variations on the above-described molding process yieldexpanded polystyrene constructs having differing characteristics and awide variety of uses. That is, instead of following all of the foregoingsteps of the illustrated embodiment, one can terminate the moldingprocess upon producing the first intermediate product, which is highdensity, unfixed (i.e., it spontaneously and partially expands somewhatto its original volume), with high memory (i.e., high resistance tobeing crushed under compression). Such constructs are suitable formolded shape parts for supporting weight, such as as a base under auni-molded shower stall or a motor vehicle dashboard. The firstintermediate product is also useful as acoustical and thermalinsulation, wherein high impact resistance is ordinarily not required,but the ability to mold a substantially hemispherical shape by a single,integrated molding process may nevertheless be highly desirable.Alternatively, one can go on to remold the first intermediate product,which yields a high density, fixed construct with low memory. Such aconstruct is suitable for molded shape parts that 778 require greatstructural strength; examples include surf board cores and industrialin-line assembly trays. One can proceed further to back fill thecontruct, yielding a combination high density layer and back-filled lowdensity layer; such constructs are suitable for energy-absorbing moldedshape parts, such as motorcyle safety helmet liners and corner pads. Onecan proceed still farther to produce a combination high density, fixedlayer with a back-filled, low density layer; such constructs aresuitable, for example, for bicycle safety helmets, box-less clamshellpackaging, and for the energy-absorbing component of a DRIVET® systemfor stucco-covered wall construction. Thus, while the preferredembodiment of the invention has been illustrated and described, it isaccordingly intended that the disclosure be taken as illustrative onlyand not limiting in scope, and that the scope following claims.

I claim:
 1. A process for molding an expanded polystyrene bead constructwithin a mold assembly, said mold assembly including a female half moldhaving a first, continuous, peripheral edge surface and an interiorsurface configured to impart a desired exterior surface to theconstruct, a male half mold having a second, peripheral edge surface inmating alignment with the first peripheral edge surface when the femalehalf mold and the male half mold are aligned on an alignment axis, afirst male mold insert mountable on the male half mold and having athird, beveled, continuous peripheral edge surface, the female half moldand the first male mold defining a first volume therebetween when thefirst male mold is inserted into the female half mold, and a second malemold insert mountable on the first male mold insert, the female halfmold and the second male mold insert defining a second, reduced volumetherebetween when the second male mold insert is inserted into thefemale half mold, the process comprising: (a) filling the female halfmold with pre-expanded polystyrene beads of a predetermined density; (b)mounting the first male mold insert on the male half mold; (c) moldingthe beads under applied heat and pressure by forcing the first male moldinsert against the beads to fuse the beads together to form a firstintermediate product of a first volume having a continuous, beveled edgesurface formed between the beveled edge surface of the first male moldinsert and the peripheral edge surface of the female half mold; (d)rapidly cooling the fused first intermediate product to within asubplasticizing temperature range to cause lower than atmosphericpressure within the beads of the first intermediate product; (e)mounting the second male mold insert on the first male mold insert; and(f) compressing the cooled first intermediate product between the secondmale mold insert and the female half mold to a second, reduced volumebefore the low pressure conditions within the beads equilibrate toambient conditions to produce a fused expanded bead body of at least 200percent higher density than the predetermined density of thepre-expanded beads.
 2. A process for molding an expanded polystyrenebead construct within a mold assembly, said mold assembly including afemale half mold having a first, continuous, peripheral edge surface andan interior surface configured to impart a desired exterior surface tothe construct, a male half mold having a second, peripheral edge surfacein mating alignment with the first peripheral edge surface when thefemale half mold and the male half mold are aligned on an alignmentaxis, a first male mold insert mountable on the male half mold andhaving a third, beveled, continuous peripheral edge surface, the femalehalf mold and the first male mold defining a first volume therebetweenwhen the first male mold is inserted into the female half mold, and asecond male mold insert mountable on the first male mold insert, thefemale half mold and the second male mold insert defining a second,reduced volume therebetween when the second male mold insert is insertedinto the female half mold, the process comprising: (a) filling thefemale half mold with pre-expanded polystyrene beads of a predetermineddensity; (b) mounting the first male mold insert on the male half mold;(c) molding the beads under applied heat and pressure by forcing thefirst male mold insert against the beads to fuse the beads together toform a first intermediate product of a first volume having a continuous,beveled edge surface formed between the beveled edge surface of thefirst male mold insert and the peripheral surface of the female halfmold; (d) rapidly cooling the fused first intermediate product to withina subplasticizing temperature range to cause lower than atmosphericconditions within the beads of the first intermediate product; (e)mounting the second male mold insert on the first male mold insert; (f)compressing the cooled first intermediate product between the secondmale mold insert and the female half mold to a second, reduced volumebefore the low pressure conditions within the beads equilibrate toambient conditions to produce a fused expanded bead body of at least 200percent higher density than the predetermined density of thepre-expanded beads; and (g) remolding the cooled intermediate productunder heat and compression between the second male mold insert and thefemale half mold to a second, reduced volume before the low pressureconditions within the beads equilibrate to ambient conditions to producea fused expanded bead body of at least 200 percent higher density thanthe predetermined density of the pre-expanded beads.
 3. A process formolding a layered, expanded polystyrene bead construct within a moldassembly, said mold assembly including a female half mold having afirst, continuous, peripheral edge surface and an interior surfaceconfigured to impart a desired exterior surface to the construct, a malehalf mold having a second, peripheral edge surface in mating alignmentwith the first peripheral edge surface when the female half mold and themale half mold are aligned on an alignment axis, the male half moldhaving an exterior surface configured to impart a desired interiorsurface to the construct, a first male mold insert mountable on the malehalf mold and having a third, beveled, continuous peripheral edgesurface, the female half mold and the first male mold defining a firstvolume therebetween when the first male mold is inserted into the femalehalf mold, and a second male mold insert mountable on the male halfmold, the female half mold and the second male mold insert defining asecond, reduced volume therebetween when the second male mold insert isinserted into the female half mold, the process comprising: (a) fillingthe female half mold with pre-expanded polystyrene beads of apredetermined density; (b) mounting the first male mold insert on themale half mold; (c) molding the beads under applied heat and pressure byforcing the first male mold insert against the beads to fuse the beadstogether to form a first intermediate product of a first volume having acontinuous, beveled edge surface formed between the beveled edge surfaceof the first male mold insert and the peripheral surface of the femalehalf mold; (d) rapidly cooling the fused first intermediate product towithin a subplastizigin temperature range to cause lower thanatmospheric conditions within the beads of the first intermediateproduct; (e) mounting the second male mold insert on the first male moldinsert; (f) compressing the cooled first intermediate product betweenthe second male mold insert and the female half mold to a second,reduced volume before the low pressure conditions within the beadsequilibrate to ambient conditions to produce a fused expanded bead bodyof at least 200 percent higher density than the predetermined density ofthe pre-expanded beads; (g) removing the second male mold insert and thefirst male mold insert from the male half mold; and (h) addingpre-expanded polystyrene beads to the mold assembly and remolding theadded beads between the female half mold and the male half mold underheat and compression to cause fusion of the added beads at an interfaceto the expanded bead body to form a layered construct comprising atleast two layers of beads wherein the layers have different densities.4. A process for molding a layered expanded polystyrene bead constructwithin a mold assembly, said mold assembly including a female half moldhaving a first, continuous, peripheral edge surface and an interiorsurface configured to impart a desired exterior surface to theconstruct, a male half mold having a second, peripheral edge surface inmating alignment with the first peripheral edge surface when the femalehalf mold and the male half mold are aligned on an alignment axis, themale half mold having an exterior surface configured to impart a desiredinterior surface to the construct, a first male mold insert mountable onthe male half mold and having a third, beveled, continuous peripheraledge surface, the female half mold and the first male mold defining afirst volume therebetween when the first male mold is inserted into thefemale half mold, and a second male mold insert mountable on the malehalf mold, the female half mold and the second male mold insert defininga second, reduced volume therebetween when the second male mold insertis inserted into the female half mold, the process comprising: (a)filling the female half mold with pre-expanded polystyrene beads of apredetermined density; (b) mounting the first male mold insert on themale half mold; (c) molding the beads under applied heat and pressure byforcing the first male mold insert against the beads to fuse the beadstogether to form a first intermediate product of a first volume having acontinuous, beveled edge surface formed between the beveled edge surfaceof the first male mold insert and the peripheral surface of the femalehalf mold; (d) rapidly cooling the fused first intermediate product towithin a subplasticizing temperature range to cause lower thanatmospheric conditions within the beads of the first intermediateproduct; (e) mounting the second male mold insert on the first male moldinsert; (f) compressing the cooled first intermediate product betweenthe second male mold insert and the female half mold to a second,reduced volume before the low pressure conditions within the beadsequilibrate to ambient conditions to produce a fused expanded bead bodyof at least 200 percent higher density than the predetermined density ofthe pre-expanded beads; (g) remolding the cooled intermediate productunder heat and compression between the second male mold insert and thefemale half mold to a second, reduced volume before the low pressureconditions within the beads equilibrate to ambient conditions to producea fused expanded bead body of at least 200 percent higher density thanthe predetermined density of the pre-expanded beads; (h) removing thesecond male mold insert from the first male mold insert; and (i) addingpre-expanded polystyrene beads to the mold assembly and remolding theadded beads between the female half mold and the male half mold underheat and compression to cause fusion of the added beads at an interfaceto the expanded bead body to form a layered construct comprising atleast two layers of beads wherein the layers have different densities.5. The process of claim 1, 2, 3, or 4, wherein the beveled edge surfaceof the first male mold insert is deviated at least 45 degrees, but notmore than 60 degrees, from a mold parting line normal to the alignmentaxis.
 6. A mold assembly for molding an expanded polystyrene beadconstruct, comprising: (a) a female half mold having a first,continuous, peripheral edge surface and an interior surface configuredto impart a desired exterior surface to the construct; (b) a male halfmold having a second, peripheral edge surface in mating alignment withthe first peripheral edge surface when the female half mold and the malehalf mold are aligned on an alignment axis; (c) a first male mold insertmountable on the male half mold and having a third, beveled, continuousperipheral edge surface, the female half mold and the first male molddefining a first volume therebetween when the first male mold isinserted into the female half mold; and (d) a second male mold insertmountable on the first male mold insert, the female half mold and thesecond male mold insert defining a second, reduced volume therebetweenwhen the second male mold insert is inserted into the female half mold.7. The mold assembly of claim 5, wherein the first male mold insert hasa plurality of upstanding alignment pins and the female half mold has aplurality of first apertures in mating alignment with said pins, wherebysaid first apertures receive said pins when the first male mold insertis mounted on the male half mold and is inserted into the female halfmold.
 8. The mold assembly of claim 6, wherein the second male moldinsert has a plurality of second apertures in mating alignment with saidpins, whereby said second apertures receive said pins when the secondmale mold insert is mounted on the first male mold insert.
 9. The moldassembly of claim 7, wherein an exterior surface of the male half moldis configured to impart a desired interior surface to a construct moldedwithin said mold assembly.
 10. A layered volume-stable expandedpolystyrene bead construct, the construct produced by a molding processwithin a mold assembly, said mold assembly including a female half moldhaving a first, continuous, peripheral edge surface and an interiorsurface configured to impart a desired exterior surface to theconstruct, a male half mold having a second, peripheral edge surface inmating alignment with the first peripheral edge surface when the femalehalf mold and the male half mold are aligned on an alignment axis, themale half mold having an exterior surface configured to impart a desiredinterior surface to the construct, a first male mold insert mountable onthe male half mold and having a third, beveled, continuous peripheraledge surface, the female half mold and the first male mold defining afirst volume therebetween when the first male mold is inserted into thefemale half mold, and a second male mold insert mountable on the malehalf mold, the female half mold and the second male mold insert defininga second, reduced volume therebetween when the second male mold insertis inserted into the female half mold, and said process comprising: (a)filling the female half mold with pre-expanded polystyrene beads of apredetermined density; (b) mounting the first male mold insert on themale half mold; (c) molding the beads under applied heat and pressure byforcing the first male mold insert against the beads to fuse the beadstogether to form a first intermediate product of a first volume having acontinuous, beveled edge surface formed between the beveled edge surfaceof the first male mold insert and the peripheral surface of the femalehalf mold; (d) rapidly cooling the fused first intermediate product towithin a subplasticizing temperature range to cause lower thanatmospheric conditions within the beads of the first intermediateproduct; (e) mounting the second male mold insert on the first male moldinsert; (f) compressing the cooled first intermediate product betweenthe second male mold insert and the female half mold to a second,reduced volume before the low pressure conditions within the beadsequilibrate to ambient conditions to produce a fused expanded bead bodyof at least 200 percent higher density than the predetermined density ofthe pre-expanded beads; (g) removing the second male mold insert fromthe first male mold insert; and (h) adding pre-expanded polystyrenebeads to the mold assembly and remolding the added beads between thefemale half mold and the male half mold under heat and compression tocause fusion of the added beads at an interface to the expanded beadbody to form a layered construct comprising at least two layers of beadswherein the layers have different densities.
 11. The construct of claim10, wherein the construct is a safety helmet.
 12. The construct of claim10, wherein the construct is an edge protector.
 13. The construct ofclaim 10, wherein the construct is a corner protector.
 14. The constructof claim 10, wherein the construct is a packing crate.